1. Field of the Invention
The present invention relates to fingerprint recording systems ad more particularly to a method of enhancing the resolution of the recorded fingerprints.
2. Description of the Prior Art
The art of fingerprinting and identifying persons by their fingerprints is well known. Both ink and inkless methods of taking a person's fingerprints are in widespread use. Either a colored ink or a colorless reagent is applied to an individual's fingers and subsequently the fingers are rolled (or pressed) into a clean recording surface, such as paper, to deposit the ink or reagent on the surface in a pattern corresponding to the individual's fingerprints. In the inkless method, an additional chemical or reagent is applied to the surface to develop the print so that it is visible. See, for example, U.S. Pat. No. 4,262,623 assigned to the assignee of the present application.
Fingerprints are conventionally taken on fingerprint cards which have been standardized by many governmental agencies such as the U.S. Federal Bureau of Investigation. Such cards normally contain the prints of the individual fingers of each hand.
For efficient recordation purposes the cards may be (1) optically read and the information thereon converted to geometric figures or digital data and stored in a computer memory or (2) photographed and stored on microfilm. With either type of recording system there is need for a clear print of high contrast (between the ridge endings and ridge bifurcations (minutiae) of each person's fingerprint. In addition, the fingerprint patterns on the cards may be transmitted via a facsimile machine.
It has been discovered that the conventional optical readers (using silicon detectors), photographic film (for microfilm recorders) and facsimile transmission apparatus have a peak of photopic response or spectral sensitivity at a wavelength of about 550 nanometers (nm) in the visible yellowish-green region. In each case the light source used to illuminate the fingerprint cards generates some ultraviolet light.